1. Field of the Invention
This invention relates to a reading method of a two-dimensional bar code, especially to a reading method of a two-dimensional bar code that facilitates both size reduction of a reading device and rapid reading.
2. Description of the Related Art
The Intacta code developed by the Intacta Loves Limited of the United States has been known as one of two-dimensional bar code systems. The Intacta code comprises black and white two-dimensional dot patterns. It is able to store high-density information, compared to a one-dimensional bar code. Therefore, it is possible to store multi-media information including musical data, image data, and text image data by coding them and utilizing a piece of paper with the Intacta code printed as an information-recording medium. The quantity of the information the Intacta code can store depends on the density of the dot patterns. The finer the dots (also called pixel elements) are, the more information can be stored.
The one-dimensional bar code is used for inventory management as well as sales management of merchandise, as it is placed on a variety of merchandise. However, since the quantity of the information stored in the one-dimensional bar code is limited, for example, only a search code of the merchandise can be recorded. The access to the vast amount of the data stored in the database is made based on the search code.
However, the information quantity the Intacta code can store in 1 cm2 is about from 400 to 500 bites, making it possible to store a vast amount of merchandise information on a piece of paper. Therefore, it is one of advantages of the Intacta code that there is no need to establish an outside database.
A line sensor such as scanner has been used to read the Intacta code printed on a piece of paper. The Intacta code captured by the line sensor is then converted into digital data and inputted, for example, into a personal computer, where the original information of the Intacta code is reproduced by executing a reproduction program. The reproduction program for the Intacta code is widely available through the Internet.
As described above, the line sensor such as scanner is used to read the Intacta code printed on a piece of paper, which requires a driver circuit to operate the line sensor itself, leading to a complicated and enlarged reading device. Also, the reading is performed by scanning the lines one by one, making the reading speed very slow.
This invention is, therefore, directed to the size reduction of the reading device and to the improvement of the reading speed, by using an area sensor for reading the Intacta code.
However, when the focal distance of a lens mounted on the area sensor for reading the code is set to be short for the size reduction of the reading device, the projected image of the Intacta code has distortion and bright spots (brightness imbalance), preventing an accurate reproduction of the recorded information. There are two possible solutions to this problem, i.e., to make the focal distance longer or to reduce the information quantity of the Intacta code. However, the former solution will achieve the size reduction, and the latter solution will hinder the advantages of the Intacta code.